Abstract
Twelve generic names have been ascribed to the New World tamarins but all are currently placed in just one: Saguinus Hoffmannsegg, 1807. Based on geographical distributions, morphology, and pelage patterns and coloration, they have been divided into six species groups: (1) nigricollis, (2) mystax, (3) midas, (4) inustus, (5) bicolor and (6) oedipus. Molecular phylogenetic studies have validated five of these groups; each are distinct clades. Saguinus inustus is embedded in the mystax group. Genetic studies show that tamarins are sister to all other callitrichids, diverging 15−13 Ma. The small-bodied nigricollis group diverged from the remaining, larger tamarins 11−8 Ma, and the mystax group diverged 7−6 Ma; these radiations are older than those of the marmosets (Callithrix, Cebuella, Mico), which began to diversify 6−5 Ma. The oedipus group diverged from the midas and bicolor groups 5−4 Ma. We review recent taxonomic changes and summarize the history of the generic names. Taking into account the Late Miocene divergence time (11−8 Ma) between the large- and small-bodied tamarin lineages, the small size of the nigricollis group species when compared with other tamarins, and the sympatry of the nigricollis group species with the larger mystax group species, we argue that the nigricollis group be recognized as a distinct genus: Leontocebus Wagner, 1839.

The tamarins are very largely Amazonian, extending outside of the basin only into the Guianas (midas group) and northern Colombia and Panama (oedipus group).

Nigricollis group – south of the ríos Caquetá, Caguán and Orteguaza, south through Ecuador and Peru, east of the Andes, to about 16°S in Bolivia, and east to the Rio Ji-Paraná in the state of Rondônia, Brazil.

Mystax/inustus group – south of the Rio Solimões-Amazonas, east of the Río Ucayali, extending east to the Rio Madeira, east and south to the ríos Urubamba and Inuya in Peru, and as far as the southern bank of the Río Muyumanu in Bolivia, with inustus between the Rio Negro and the Rio Solimões, extending west into Colombia.

Midas/bicolor groups – Guiana Shield, east of the rios Negro and Branco and the Essequibo River in Guyana, north of the Rio Amazonas, and east of the Rio Xingu, south of the Rio Amazonas.

Oedipus group – northern Colombia, basins of the ríos Cauca and Magdalena, and Panama.